#include "stdafx.h"
#include "rc4.h"

static void
swap_byte (unsigned char *a, unsigned char *b)
{
	unsigned char swapByte;

	swapByte = *a;
	*a = *b;
	*b = swapByte;
}

void
prepare_key (unsigned char *key_data_ptr, int key_data_len, RC4_KEY *key)
{
	unsigned char index1;
	unsigned char index2;
	unsigned char *state;
	unsigned int counter;

	state = &key->state[0];
	for (counter = 0; counter < 256; counter++)
		state[counter] = counter;
	key->x = 0;
	key->y = 0;
	index1 = 0;
	index2 = 0;
	for (counter = 0; counter < 256; counter++)
	{
		index2 = (key_data_ptr[index1] + state[counter] + index2) % 256;
		swap_byte (&state[counter], &state[index2]);

		index1 = (index1 + 1) % key_data_len;
	}
}

void
rc4 (unsigned char *buffer_ptr, unsigned buffer_len, RC4_KEY *key)
{
	unsigned char x;
	unsigned char y;
	unsigned char *state;
	unsigned char xorIndex;
	unsigned int counter;

	x = key->x;
	y = key->y;

	state = key->state;
	for (counter = 0; counter < buffer_len; counter++)
	{
		x = (x + 1) % 256;
		y = (state[x] + y) % 256;
		swap_byte (&state[x], &state[y]);

		xorIndex = (state[x] + state[y]) % 256;

		buffer_ptr[counter] ^= state[xorIndex];
	}
	key->x = x;
	key->y = y;
}